Multiple OmniFocus Documents

When you first open OmniFocus (OSX), the loading indicator says “Opening OmniFocus document…”

Could that mean it’s possible to have multiple OF “documents” (such as Personal and Work) and open them separately?

IIRC, there is only one main OmniFocus database. But you can open an OmniFocus database backup to recover data.

You can also go to File > Open Archive and see your old completed tasks that you have archived. This will open up a new window showing your archived projects/tasks.

With some limitations, it is perfectly possible to use multiple OF files and open them separately. It is discussed here:
Having 2 separate OmniFocus 2 apps